真江蓠(Gracilaria verrucosa)对网箱养殖海区的生态修复及生态养殖匹配模式

2006年8～9月,在浙江象山港花鲈(Lateolabrax japonicus)养殖网箱中吊养真江蓠(Gracilaria verrucosa)对网箱养殖造成的水体富营养化进行生态修复研究.通过45d内的平面监测、定点跟踪监测和断面监测,结果表明:该网箱养殖区水体呈严重富营养化状态,营养状态指数(E)为32.00,其营养盐分布由高浓度的中心区向周围150m非养殖水域扩散;真江蓠对养殖区的富营养化海水具有较好的修复效果:江蓠生态修复区及其相邻网箱中水体PO4-P、NO2-N、NH4-N和NO3-N含量显著低于非修复区(P＜0.01),修复区海水PO4-P、NO2-N、NH4-N和NO3-N浓度比非修复区分别降低22%～58%、24%～48%、22%～61%和24%～47%.养殖真江蓠45d后,修复区水体DO浓度和透明度显著高于非修复区(P＜0.05),DO平均提高28%,透明度平均提高30%;而修复区水体Chl-a浓度显著低于非修复区(P＜0.05),平均降低49%.通过建立基于N平衡的鱼藻生态养殖模式,每收获1kg花鲈至少需要匹配江蓠4.7 kg wet wt才可实现对鱼类排放N的完全吸收.因此网箱内栽培江蓠的混合生态养殖模式,可平衡因经济动物养殖所带来的额外营养负荷,有利于实现动物养殖环境的自我修复.

Bioremediation of caged fish aquaculture by the red alga Gracilaria verrucosa in an integrated multi-trophic aquaculture system

Gracilaria verrucosa (Huds.) Papenf. was cultured on ropes in close proximity to the caged fish aquaculture of Lateolabrax japonicus in Xiangshan Harbor, Zhejiang Province, China during the summer of 2006. Prior to the start of the integrated multi-trophic aquaculture (IMTA) of Gracilaria with Lateolabrax, water quality was monitored at 220 sampling points ranging from a minimum of 20 to a maximum of 150 m from the fish pens. Levels of dissolved inorganic nitrogen (NO2-N, NH4-N and NO3-N), phosphate (PO4-P) and chemical oxygen demand (COD) in the water column were 0.053 mg L-1, 0.36 mg L-1, 0.64 mg L-1, 0.086 mg L-1 and 1.59 mg L-1, respectively. The index of eutrophication reached 32.00. After 45-days of cultivation of Gracilaria near the fish cages, the average concentrations of PO4-P, NO2-N, NH4-N and NO3-N were reduced by 22%-58%, 24%-48%, 22%-61% and 24%-47%, respectively. In addition to the reductions of nitrogen and phosphorus, there was a 28% increase in the concentration of dissolved oxygen and a 30% increase in the transparency of seawater in areas where Gracilaria was cultured with Lateolabrax. There was also a 49% reduction in chlorophyll a in these areas. Biomass of Gracilaria after 45 days of culture in association with the fish aquaculture was (7.80±1.65) kg m-1 and Gracilaria had a maximum SGR of 13.2% d-1. Nitrogen content in dry thalli harvested from the fish cages averaged 4.80%. According to the nitrogen budgets of L. japonicus and G. verrucosa in open mariculture system, 4.7 kg wet wt cultivated G. verrucosa are needed to balance the nitrogen discharged by 1 kg harvested L. japonicus. The integration of the Gracilaria culture with finfish aquaculture in an integrated multi-trophic aquaculture (IMTA) system is an effective practice for nutrient bioremediation of coastal waters that will also result in economic diversification by producing another value-added marine crop.